Device and method for detecting overlapping objects

Abstract

Device for detecting overlapping objects in a stream of transported flat objects in a transport path that comprises a measurement path, in which use is made of a braking roller in the measurement path. The device furthermore comprises a sensor for the passing speed of objects. If there are overlapping objects in the measurement path, the effect of a deceleration by the braking roller on the passing speed will be greater than if just one object is present in the measurement path, on account of the decelerated object lagging behind relative to the rest of the series of overlapping objects.

1. Device for detecting overlapping objects in a transport path for flat objects, such as letters etc., whereby the transport path comprises a measurement path, in which measurement path a braking device is located by which a passing object or an object from a series of overlapping passing objects is decelerated in the measurement path, wherein the device comprises:
 a detection means in the measurement path for observing a passing object or an object from a series of overlapping passing objects, which detection means emits a presence signal in response to the presence of a passing object or an object from a series of overlapping passing objects, and  
 a sensor in the measurement path, the emitted signal of which is a measure for the passing speed of an object or of an object from a series of overlapping passing objects,  
 while the braking device comprises a braking roller, which in the presence of an object in the measurement path is in contact with that object, and the braking device is arranged such that the braking roller is decelerated during a predetermined first time span between the beginning and the end of the presence signal and in a predetermined manner, whereby the device comprises means to determine the change in passing speed resulting from the deceleration of the braking roller.  
 
   
   
     2. Device according to  claim 1 , wherein the braking device is arranged such that the deceleration of the braking roller during the predetermined first time span is effected by decelerating the braking roller at least once, during a predetermined second time span. 
   
   
     3. Device according to  claim 1 , wherein the braking roller is covered with friction material. 
   
   
     4. Device according to  claim 1 , wherein the braking device comprises an electric motor switched as a dynamo, as well as control means at whose command the dynamo is short-circuited during the predetermined first time span at least once for a second time span. 
   
   
     5. Device according to  claim 1 , wherein the device furthermore comprises thickness measuring means, which thickness measuring means are arranged to emit a thickness signal that is a measure for the thickness of an object, or of a series of overlapping objects, in the transport path, whereby the braking device is arranged such that, depending on the thickness signal, the braking roller is decelerated for a shorter or longer time. 
   
   
     6. Device according to  claim 2 , wherein the braking roller is covered with friction material. 
   
   
     7. Device according to  claim 2 , wherein the braking device comprises an electric motor switched as a dynamo, as well as control means at whose command the dynamo is short-circuited during the predetermined first time span at least once for a second time span. 
   
   
     8. Device according to  claim 3 , wherein the braking device comprises an electric motor switched as a dynamo, as well as control means at whose command the dynamo is short-circuited during the predetermined first time span at least once for a second time span. 
   
   
     9. Method for detecting overlapping objects in a transport path for flat objects, such as letters etc., whereby the transport path comprises a measurement path, in which measurement path a braking device is located by which a passing object or an object from a series of overlapping passing objects is decelerated in the measurement path, wherein the following are also included in the measurement path:
 a detection means for observing a passing object or an object from a series of overlapping passing objects, which detection means emits a presence signal in response to the presence of a passing object or an object from a series of overlapping passing objects, and  
 a sensor, the emitted signal of which is a measure for the passing speed of an object or of an object from a series of overlapping passing objects,  
 whereby the braking device comprises a braking roller, which in the presence of an object in the measurement path is in contact with that object, and whereby the method comprises the following steps:  
 a) the measurement to detect overlapping objects is started at the moment that the presence of an object is established by the detection means;  
 b) the braking roller is decelerated during a predetermined time span between the beginning and the end of the presence signal and in a predetermined manner;  
 c) with the aid of the sensor for the passing speed, the amount by which the passing speed decreases during the deceleration of the braking roller is determined;  
 d) this amount is compared with a predetermined threshold value;  
 e) if the amount is higher than the threshold value, it is assumed that a series of overlapping objects is present and an overlap signal is generated, and if the amount is lower than or equal to the threshold value, it is assumed that there is no series of overlapping objects present and no overlap signal is generated.  
 
   
   
     10. Method according to  claim 9 , wherein the deceleration of the braking roller during the predetermined first time span is effected by decelerating the braking roller at least once, during a predetermined second time span. 
   
   
     11. Method according to  claim 9 , wherein the braking roller is covered with friction material. 
   
   
     12. Method according to  claim 9 , wherein the braking device comprises an electric motor switched as a dynamo, as well as control means for short-circuiting the dynamo and whereby the deceleration of the braking roller is effected by short-circuiting the dynamo. 
   
   
     13. Method according to  claim 9 , wherein the device furthermore comprises thickness measuring means, which thickness measuring means are arranged to emit a thickness signal that is a measure for the thickness of an object, or of a series of overlapping objects, in the transport path, whereby during the period between the beginning and the end of the presence signal the braking roller is pressed more or less strongly against passing objects, depending on the thickness signal. 
   
   
     14. Method according to  claim 10 , wherein the braking roller is covered with friction material. 
   
   
     15. A device for detecting overlapping flat objects, said device comprising:
 a measurement path along which a moving object passes;  
 a braking device for decelerating said object in said measurement path;  
 a detector in said measurement path that detects said moving object and emits a presence signal in response to the presence of said moving object;  
 a sensor in said measurement path that emits a speed signal that is a measurement of a speed of said object passing said sensor,  
 wherein said braking device comprises a braking roller that directly contacts said object, said braking device is structured and arranged so that said braking roller is decelerated during a first time period between a beginning and an end of the presence signal, such that the device determines a change in the passing speed based on the deceleration of the braking roller.